High-performance glass substrates that have superior optical performance (transmittivity, etc.) and mechanical performance (flatness, etc.) are used in flat panel displays, for example. However, they are expensive, so if the thin metal films formed upon their surfaces do not satisfy quality control standards, it is preferable to remove the thin metal films and reuse the substrates.
Methods of removing these thin metal films include the method of removal by chemical etching. As shown in FIG. 18, this method is one wherein a substrate 2 that has formed on its surface a thin metal film that is to be removed is immersed in a chemical solution 1 that can dissolve the thin metal film by a chemical reaction, thus removing the thin metal film (see the publications of unexamined Japanese patent application (Kokai) Nos. JP-A-H6-321581 and JP-A-H9-86968, for example).
However, the method of removal by chemical etching requires the use of strongly acidic or strongly alkaline chemical solutions, and thus has the following problems.                1) Great care must be taken in its handling, worsening the work productivity.        2) The apparatus must be made corrosion-resistant and is thus expensive.        3) The chemical solution is basically not reusable, giving large amounts of waste.        4) After use, disposal of the waste liquid from the chemical solution is difficult.        
The present invention came about in consideration of the aforementioned problems with the prior art, and has as its object to provide a method that is able to efficiently remove thin metal films basically in a non-contact manner without the use of strongly acidic or strongly alkaline chemical solutions, and that does not require precise positional control, and an apparatus for implementing this method.